The present invention relates generally to an implantable stimulation lead for use with an implantable pulse generator such as a cardiac pacemaker and, more specifically to such an implantable stimulation lead with the capability of anchoring an electrically active helix electrode at a desired site when the lead is fixated in the heart.
Currently, known extendable/retractable screw-in implantable stimulation leads have an electrically active helix electrode. The helix electrode is directly connected to the distal coil conductor for the electrical connection and the extendable/retractable mechanism. In this design, the electrically active helix is intermittently in contact with the distal housing wherein the helix electrode resides. Therefore, in order to prevent chatter noises generated from the intermittent contacts between the helix and the distal housing, the distal housing must be of a nonconductive material such as plastic or ceramic. In this instance, since the distal tip is not electrically active during the lead implantation, in order to verify the pacing threshold and sensing amplitudes, the helix must be extended and fixated to the heart tissue. However, if the electrical measures are not acceptable, the helix must be retracted and again extended for fixation to a different implant site. This is considerably time consuming and inconvenient for the patient and for the implanter as well. To improve this situation, an electrically active mapping collar is incorporated onto the distal tip of the lead. This construction enables the implanter to choose an acceptable implant site before extending and fixating the helix to the final implant location. However, if the helix and housing collar are not continuously connected electrically, electrical noises or xe2x80x9cchatterxe2x80x9d would be generated from the intermittent contacts between the helix and distal housing and the lead would not be clinically acceptable. The chatter-free contact spring designs presented below will prevent the problem from occurring.
Typical of the known prior art is commonly assigned U.S. Pat. No. 5,447,533 to Vachon et al., which discloses a helix electrode system employed with an implantable stimulation lead.
It was in light of the foregoing that the present invention was conceived and has now been reduced to practice.
An implantable endocardial lead is disclosed for use with a cardiac stimulation device. The lead includes an electrical conductor whose proximal end is coupled to an electrical connector. An active fixation electrode is coupled to the distal end of the conductor, being movable between a retracted position fully within the lead and an extended position advanced beyond the distal end of the lead for effecting penetration into the myocardial tissue. A resilient coupling mechanism maintains electrical continuity between the active fixation electrode and the electrically active housing throughout movement of the active fixation electrode between the retracted position and the extended position. In one instance, a conductive coupling is slidably received on a conductive shaft and is fixed to the electrically active housing. A compression spring is received on the conductive shaft intermediate and engaged with the conductive coupling and with a conductive stopper including a ring member fixed to the conductive shaft and projecting radially from its longitudinal axis to a peripheral rim beyond the outer surface of the conductive shaft. In another instance, an annular track member integral and in electrical continuity with the electrically active housing has an annular recess surrounding the conductive shaft and a metallic coil spring received in the annular recess and slidably engageable with the conductive shaft.
Thus, in order to prevent the xe2x80x9celectrical chatterxe2x80x9d problem described above generated by two electrically conductive parts (a helix electrode and a conductive housing) in intermittent contact, in one embodiment a compression contact spring is used to provide a positive electrical connection between the two electrically active and moving parts. In an alternative design, a xe2x80x9cball sealxe2x80x9d type contact spring can also be used for the same purpose.
Accordingly, a primary feature of the invention is to provide an implantable stimulation lead in which the electrically active helix electrode of an extendable/retractable design is continuously in contact with the distal housing in which the helix electrode resides.
Another feature of the present invention is to provide such an implantable stimulation lead which is of a xe2x80x9cchatter-freexe2x80x9d construction.